Hydrogen density-of-states distribution in zinc oxide

The presence of hydrogen in zinc oxide gives rise to n-type conductivity. Hydrogen effusion measurements performed on single-crystal ZnO and sputtered ZnO films directly reveal H concentrations of about 5.2×10¹⁶cm^-3 and up to 3.0×10²¹cm^-3, respectively. From the hydrogen effusion spectra the hydrogen chemical potential μH is determined as a function of the H concentration, which can be related to the hydrogen density-of-states distribution. State-of-the-art single-crystal ZnO shows six peaks in the H density of states located between 0.59 eV and 1.4 eV below the H transport states. On the other hand, in sputtered ZnO the majority of the hydrogen (≈75%) has binding energies larger than 1.0 eV.